[gtk2] add for Gtk::TreeViewColumn#set_sort_column_id for GTK+ < 2.18.
[gtk2] add for Gtk::TreeViewColumn#set_sort_column_id for GTK+ < 2.18.

[ruby-gnome2-devel-en] Gtk::TreeViewColumn
Reported by grant schoep. Thanks!!!

kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2,kitachro/ruby-gnome2